It is tempting to reject incrementism on the grounds that new objects may be brought into existence by giving existing objects certain features that are contingent to them. For example, we seem to bring an object into existence by manipulating a wad of clay so that it takes a sundial shape. One argument that supports this criticism of incrementism presumes that things compose objects by virtue of being simply bonded. But while something along these lines may seem plausible as regards composition at a time, it is not promising at all as regards persistence, or composition over time. Another argument presumes that a wide range of count nouns, favored count nouns such as “sundial,” pick out objects – that the features that suffice for some things to fall under some such count noun also suffice for those things to compose an object. It turns out, however, that things that clearly do not compose objects may, together, fall under “sundial,” and the same is likely to be true of other favored count nouns. Instead of rejecting incrementism, I suggest that when we give existing object features that are contingent to them we bring no new objects into the world.

In this chapter, I clarify what it is for a composite object to exist at a time and over time by analyzing the conditions under which things compose it at a time and over time. Some things, the xs, make up an object, O, at a time t1 if and only if the xs are maximally bonded then, which is to say that the xs are simply bonded, clinging together, and include everything simply bonded to any of the xs. The object O that is composed of the xs at one time may be made up of other things at a subsequent time. Over time, however, objects may change in composition only incrementally (unless we allow for the possibility of an object being disassembled then reassembled). Incremental changes are ones in which the mass of what is added (removed) is small as compared to the object’s mass before the addition (removal).

The account of organisms I offer in one chapter clashes with the account of objects I offer in another. To resolve the clash, we could say that there are two sorts of objects, mere objects with the composition and persistence conditions supplied by the incrementist account, and organisms with organismal criteria, as supplied by the integratist account. However, this solution forces us to give up the non-overlap principle, which says that objects cannot overlap: they can never be made up of the same constituents at the same time (although one may be a proper part of the other). A solution that is consistent with the non-overlap principle is to say that the criteria of composition and persistence for objects are disjunctive, in that although an object may persist organismally and incrementally at once, it may continue to survive, after ceasing to persist organismally, if it meets the incrementist criteria. To deal with possible branching cases, and to avoid the possibility of things assimilating organisms, we will also need to add that organismal criteria trump incrementist criteria.

Meaningfulness is a matter of what adds meaning to our lives. What confers positive meaning (meaning makers) on our lives is our achievements, while negative meaning results from our failures. Dying has positive meaning for us if and only if, and to the extent that, living on has negative meaning for us, and vice versa. Meaning makers are a species of welfare makers, so what gives my life meaning also makes it better for me, but it is entirely possible to have a good life that is devoid of meaning. One excellent reason to live is to achieve things, to give my life meaning, but it is not the only good reason, since I have a very clear reason to live on when the life in prospect is good for me. We need not limit our aims to things we might achieve solely as individuals. We can share goals with others, even with people who have yet to be born. In particular, we can strive, together, to develop ways in which people may enhance themselves.

Having prudential interests is a matter of possessing features, such as the ability to feel pain and pleasure, by which an organism can be concerned about itself. Some organisms lack such features. Sponges have no welfare apparatus; they are unresponsive. A responsive organism may acquire things that are intrinsically good or bad for it. These determine its welfare level, whether over a brief interval of time or over a lifetime, which, in turn, determines whether something is overall good or bad for it. An event or state of affairs E is overall good (bad) for us just if, and to the extent that, the intrinsic value for us of the actual world, in which E occurs, is higher (lower) than that of the closest world in which E does not occur. If the intrinsic value for me of a world w equals my lifetime welfare level in w, then coming into existence, and coming to be responsive, was neither good nor bad for me. If we assume that the intrinsic value for me of a world in which I am unresponsive is 0, then it was good for me to come into existence and to become responsive.

Evolution by natural selection is not a process by which objects called “species” change over time under selective pressures. There are no such objects. It is a process by which organisms that are related in salient ways, by which they are specific we might say (as opposed to being members of a species), are replaced by others. There is more than one way in which they can be specific. One is related compatibility, which some organisms, the xs, exhibit just when they have common ancestry, when they are reproductively compatible, and when every organism so related to one of the xs is among the xs. Given this way of understanding specificity, we current humans, the Homo sapiens presently inhabiting the planet, could give way to future humans that resemble us only insofar as they are reproductively compatible with us. What is more, our humanity is not essential to us. Neither is our origin, in that we might have originated in a different time and place. So in theory – given technology that is currently out of sight – we could change ourselves into creatures that are very unlike us.

Here I discuss an argument, suggested by some things that Descartes said, which appears to refute animal essentialism:

1. Suppose that being an organism is essential to me.

2. Then it is impossible for me to exist yet fail to have the features that make for being an organism.

3. If it is impossible for me to exist yet fail to have these features, and my existence is certain, for me, then it is also certain that I have these features.

4. It is certain for me that I exist.

5. But it is not certain for me that I have the features that make for being an organism.

6. 2–5 are inconsistent, so 2, and the assumption at step 1, are false. Being an organism is not essential to me.

I argue that the third premise is vulnerable to attack on the grounds that it is based on a closure principle (certainty is closed under strict implication) that, arguably, is implausible. I also argue that Premise 4 may be challenged by appealing to an account of certainty inspired by some remarks by Lichtenberg, according to which my existence is not certain for me.

This chapter introduces the book. What may we become? What is the significance of extinction? This book addresses these questions after clarifying what persons, species, organisms, and material objects are. Like you, I am an organism, but also a material object. I could survive, remaining that same object, after it stops being a human organism.

Viability is a capacity an organism’s constituents have – the ability to engage in various such as nutrition in an integrated way. It is what makes things compose an organism and what makes an organism alive. To die is to lose that capacity. So things come alive by coming to be organisms, and they die when they cease to be organisms. But in theory an object that dies while it is an organism might later be brought back to life. Since dying is the loss of viability, and nothing is viable while nonexistent, any object that ceases to exist while it is alive dies. Nor may anything be a corpse while it is still an organism. Yet objects that die while they are organisms may continue to exist – they may become corpses. So the dead may exist. Personhood is a phase objects go through while they are organisms that can think. When you and I use the term “I,” we refer to an object that is currently both an organism and a person, but the property of being a person is contingent to organisms, and the property of being an organism is contingent to us.

The view of our nature that I defend, animalism is a straightforward, plausible view that coheres well with the biological facts about human animals and with common sense. By contrast, its chief competitor, mentalism, in its various incarnations, implies that the self is a special object that bears a mysterious relation to the animals in which it is “realized.” Were it not for the strong intuition that we go with (some of) our brains when these are transplanted into other animals, animalism would stand out as the most plausible view about what we are. But our intuition is misleading. It is a mistake to think that we go with our brains when these are transplanted. What goes on in the brain tissue of human animals makes it possible for those animals to think, but, in situ, that tissue is not an object. Hence, it is not an object that can be moved to a different animal, and you and I are not (identical to) our brains.

In the future, advances in genetic modification techniques will make it possible for us to change ourselves dramatically. Should we apply these techniques to ourselves? Should we apply them to our children? In answering these questions, we are hampered by the fact that the interests of an organism are determined by its design, at least in part. Having interests is a matter of possessing features, such as the ability to feel pain and pleasure, by which an organism can be concerned about itself. So choosing our design based on our interests seems circular. Still, we can take it for granted that we will wish to change our welfare apparatus, and that of our children, only in peripheral ways, and give preference to options that make our lifetime welfare level higher than other options. Several sorts of enhancement would benefit us. For example, if we can avoid senescence, we should extend our life span.

What compose organisms at any given time are bonded things that are able to form fresh bonds to new things and to break bonds that are already in place. The activities of their constituents are organized and controlled, or integrated, under the guidance of information they carry. This is a very rough picture of what composes organisms. After sketching it out, I considered three ways of refining it – three accounts of the composition of an organism at a time and over time. The first, the gradualist account, says that an organism survives only incremental changes that leave its constituents integrated. However, organisms may survive grave injuries and radical forms of surgery that change their composition suddenly and dramatically. The second, unrefined integratist account, solves this problem, as it allows for even drastic changes in an organism’s constituents, as long as these leave them capable of activities integrated in conformity with the information that was encoded in the nucleic acid within them before the change. But the unrefined account implied that an organism could become two, and two one. To solve that problem I offer a third account, integratism, which says that an organism’s constituents can only undergo nondiverging, nonmerging replacements.